This invention relates generally to audio systems and more particularly concerns distributed audio systems for audio announcement and background music.
Distributed audio systems for audio announcement and background music are very common in airports, hotels, restaurants, shopping centers, office buildings and many other commercial buildings. For many years the common distributed sound system has used 70 or 100 volt audio systems whereby the driving power amplifier output drives the audio signal through a matching transformer and each speaker in the system also incorporates additional matching transformers allowing a large number of speakers to be installed within a given system. The system power in a 70 volt system will be reduced by losses due to cable length, transformer loss and numerous other contributing factors. These systems are limited in total output power such that the total system power cannot exceed the maximum output power of the driving power amplifier plus the typical system losses. Once the systems power amplifiers maximum output power is met additional power amplifiers are required in order to add additional speakers into the system.
One of the largest drawbacks to the typical 70 volt distributed audio systems is the audio quality. The typical distributed sound system has greatly reduced audio fidelity and clarity. Most applications of distributed audio systems require multiple zones whereby the level of each zone can be adjusted at a master point in the system and also allow adjustment of the zone level in a remote location, typically somewhere within in the zone. Adding a remote zone level control requires an expensive power attenuator which, in many systems, can easily be overloaded, increasing distortion and further reducing the fidelity of the system.
Attempts to provide improved audio performance distributed audio systems have thus far been relatively complex and expensive. One proposed system, for example, improves audio with powered speakers connected over Cat5 cable but requires on board digital signal processing (DSP) and digital-to-analog converters at each speaker. While it is desirable to offer powered speakers for improved audio and to use Cat5 cable due to the lower cost of Cat5 wire, the proposed system has several drawbacks due to the limitations of current that can be passed over Cat5 wire. The proposed system feeds low voltage DC power down a pair of the Cat5 cable wires, which results in a large voltage drop over distance due to the small gauge of the Cat5 wire. Using on board DSP and digital-to-analog converters together with power amplifiers at each speaker requires a large amount of quiescent current which becomes the base line power before audio amplification. Amplifying the audio signal to a typical level means that the total power consumption per speaker becomes excessive. Therefore, an expander power converter is required in order to increase the number of speakers to a useful level, increasing the cost and complexity of the proposed system.
It is, therefore, an object of the present invention to provide a low cost high definition distributed sound system. Another object of the invention is to provide a high definition distributed sound system having improved sonic performance in relation to previously known systems. A further object of the invention is to provide a high definition distributed sound system which permits master, remote zone and individual speaker level controls. Yet another object of the invention is to provide an easily expandable high definition distributed sound system. Still another object of the invention is to provide a high definition distributed sound system which permits incorporation of useful numbers of speakers without enhancement of the power within the interconnected speakers. Another object of the invention is to provide a high definition distributed sound system with reduced base line system power requirements. A further object of the invention is to provide a high definition distributed sound system which applies higher ratios of power consumed to drive its speakers. Still another object of the invention is to provide a high definition distributed sound system which operates within the maximum allowable low voltage AC that can be distributed in commercial applications.